1. Field of Invention
The invention relates to the design of plasma based fusion energy devices, specifically to the incorporation of apparatus for providing ionized fuel inside such devices and for improving the power balance of such devices.
2. Prior Art
The Need for Fusion Fueled Power Plants
The energy needs of the world are growing exponentially. Energy consumption is projected to double by the year 2050 and to meet these growing needs a thousand new coal-burning power plants are planned and/or under construction. These power plants will cost approximately 4 trillion dollars to build. Even worse than this expense, burning coal increases air pollution and carbon emissions. These side effects cause global warming and degrade the health of people around the world.
Nuclear power plants offer an attractive alternative to coal powered power plants. Nuclear fission reactors operate like a slow atomic (“A”) bomb, giving off energy from splitting heavy plutonium or uranium atoms into smaller atoms. France generates most of its electricity from fission reactors and has achieved a good safety record. Reactors in some other countries have not had such good safety records. Three-mile Island, Chernobyl, and Fukushima are examples of reactors which have accidentally melted down and devastated the local environment. These disastrous meltdowns have created widespread mistrust of fission reactors as a practical alternative to coal burning plants.
Nuclear fusion reactors do not melt down and do not pollute. They are designed to operate like a slow and safe hydrogen (“H”) bomb, fusing light isotopes of hydrogen, helium, and/or boron. Fusion devices are classified by the methods used to confine and heat a plasma of fuel ions mixed with electrons. Since the early 1950's, much research has been directed toward developing different fusion concepts. At this time the concept known as “tokamak” has become the favorite of the international fusion community. ITER, the latest multinational tokamak experiment, is currently under construction in the south of France. ITER will cost tens of billions of dollars to build and operate. Unfortunately, the first power plant based on ITER will not be ready until the mid-2040's at best. And worse, the complicated design of ITER makes it doubtful that it will ever be used for commercial power generation.
At a recent international fusion conference, senior D.C. Energy Adviser Robert Hirsch criticized ITER, “First, we have to recognize that practical fusion power must measure up to or be superior to the competition in the electric power industry. Second, it is virtually certain that tokamak fusion as represented by ITER will not be practical.”
ITER and other tokamak designs have serious disadvantages when compared to Inertial Electrostatic Confinement (IEC) fusion. The tokamak has a toroidal shape, leading to magneto-hydrodynamic (MHD) instabilities. Instabilities cause excessive plasma losses through the outside edge of the torus. In ongoing attempts to patch the loss points, the design of the tokamak has evolved to incorporate an expensive, super-conducting magnet design. In contrast, IEC devices confine the plasma into a quasi-spherical shape, which is MHD stable. Stability allows IEC devices to have a simpler design than ITER. By overcoming ITER's drawbacks, as pointed out by Hirsch (above), these simpler IEC designs will be more acceptable to the power industry.
One example of an IEC design intended for power production was disclosed in a 2004 U.S. Pat. No. 8,059,779 to Greatbatch. The Greatbatch patent claims, “An electrostatic fusion device, comprising: a vacuum chamber; a potential well disposed in said vacuum chamber; a partial vacuum environment in said vacuum chamber containing fusion reaction ions; . . . .” (Here ends the quotation from Greatbatch.) Unfortunately, Greatbatch's patent lacks any description of how the “fusion reaction ions” came to be inside the potential well in the first place. Getting the ions into the potential well is a big problem not dealt with in the Greatbatch patent. Without an adequate fuel supply the proposed 2004-Greatbatch device cannot produce useful energy.
The Polywell Reactor Concept
The most promising example of an IEC fusion device was disclosed in pending U.S. Pat. 2010/0284501A1 by Rogers, entirely incorporated herein by reference. The 2010-Rogers application teaches an improvement on the well-known Polywell IEC reactor design. Polywell was originally patented by Robert Bussard in 1989 U.S. Pat. No. 4,826,646. Polywell has been the subject of extensive research by Energy Matter Conversion Corporation (EMC2) of Santa Fe, N. Mex. Bussard served as the CEO of this Company until his death in 2007. The Company's research was continuously funded by the U.S. Navy from 1991 to 2014. Shortly before his death, Bussard wrote a final report documenting his concerns about the unsolved problems with Polywell.
Bussard's final report, “Polywell Results and Final Conclusions,” is hereinafter referred to as 2007-Bussard. The following excerpts from 2007-Bussard retain the same paragraph numbering as in the original report:
4. “Large scale vacuum pumping is required to avoid high-voltage arcing. But such vigorous pumping produces a core fuel density so low that it cannot produce significant fusion rates inside the machine . . . . Thus, some means must be found to ensure large electron density within the machine.”
5. “This requires that the ionization (of neutral gas) density within the machine must be very large relative to that outside; and this can be attained only by neutral gas injection directly into the machine, followed by subsequent very rapid ionization of this gas, before it can escape into the exterior region. In small machines this is difficult . . . .”
6. “Thus, in small systems there is a big incentive to attempt to fuel the machine with ions injected from ion guns . . . [but] they can not be fully magnetically shielded . . . . In this situation, it appears that the only way to test these principles in small machines is to try to use capacitor discharge drives . . . .”
11. “Thus, full-scale machines and their development will cost in the range of ca $180-200 million, depending on the fuel combination selected . . . . USNavy costs expended to date [i.e. 2007] in this program have been approximately $18 million over about 10 years . . . .”
Only one public announcement has come from EMC2 since Bussard's death in 2007. In 2014, a research paper entitled “High Energy Electron Confinement in a Magnetic Cusp Configuration” was published by EMC2. First author of the paper was Dr. Jaeyoung Park, CEO of the Company. This paper, hereinafter called 2014-Park, reports experiments confirming the existence of the “wiffle-ball effect.” Coined by Bussard in 1991, “wiffle-ball effect” is a term used to describe the diamagnetic closing of electron-loss channels at high plasma density. The existence of the wiffle-ball in Polywell is essential if the Polywell design is to be used for practical power production. Wiffle-ball was predicted theoretically by Bussard in 1991 but had not been seen experimentally until the work reported in 2014-Park. The 2014-Park paper is timely and important for validating the Polywell concept.
The machine design disclosed by this patent application goes far beyond the work reported in 2014-Park. The main flaw of the Park paper is that their experimental device operated in pulsed mode and without proper cooling. In pulsed mode, fusion energy output lasts only for a tiny fraction of a second. Net-power reactors must operate for months and years, not milliseconds. In addition, the power to heat the plasma came from external plasma guns. By nature, these guns are hopelessly inefficient for net energy production. To operate in a net-power mode, plasma-heating power must come from a high-voltage electron injector, not from a plasma injector. No high-voltage power supply was used in the work reported in 2014-Park. Without efficient plasma heating there is no hope that a Polywell device will ever produce more power than it consumes just to stay hot.
Small-scale Polywell devices always consume more power than they produce. On the other hand, building a large-scale (i.e. break-even) device would cost hundreds of millions of dollars. To attract private investors it is now necessary to build and test structurally-correct, small-scale machines. Then keeping to a proven design, larger and larger scale-models can be built. At each stage of development the performance of the scale-model reactor can be compared with computer simulations. Once tested, the simulations can then be used to predict the performance of the next larger scale-model. In this way, designing the expensive net-power machines can be approached gradually and with confidence. Polywell, when properly fueled, can reach break-even and still avoid the complexity of tokamaks.
Problems with Polywell—FIGS. 1A, 1B
Pulsed operation, as described in 2007-Bussard and 2014-Park, is inadequate for demonstrating the Polywell principle. When the machine is operated pulsed, power is produced for only a tiny fraction of a second at a time. A viable power-reactor must demonstrate long-term, steady-state operation to earn the confidence of the power companies.
FIG. 1A shows a drawing of a magnet module (200) from the prior art. This drawing is copied from FIG. 3c of 2010-Rogers. The module shown was designed for steady-state, not pulsed, operation. According to the design, six or more similar modules are mounted on the faces of a polyhedron. Inside the polyhedron a plasma of electrons and ions is confined and heated. An ion gun (460) injects ions along the axis of one of six coil magnets (410). Finding a suitable place to position the ion gun was the main problem with this design. The central axis of the magnet must be kept open to allow high-energy electrons to circulate in and out of the core. The problem was that there was no workable position for the ion gun, i.e. where it avoids being hit by electrons.
Electrons are born in an electron source (414). From the source, the electrons accelerate along the coil axis, i.e. in an upward direction in the Figure. Trapped electrons form a potential well inside the polyhedron. The potential well accelerates and traps ions born in the ion gun. The potential well has a roughly circular shape, like a volcano. Newborn ions are emitted from the source positioned at a point high on the rim of the well. The ions then fall down the inner wall of the potential well. Ions stream continuously into the core, each ion accelerated to fusion energy. Once in the core, each ion bounces many times back and forth across the well. After many passes through the center of the reactor, each ion either fuses or up-scatters out of the well. Whether lost to fusion or up-scattering, lost ions must be continuously replaced from the ion source to maintain the plasma density and temperature at constant values.
Input power to the reactor is provided by a high-voltage power supply, not shown in this Figure. The power enters the magnet on wires inside insulated legs (404). The power supply biases the magnets on all (six or more) modules to a high-voltage, typically in the range 10-500 kilovolts. The positive voltage on the magnets attracts the negatively charged electrons. Electrons accelerate from the ground-potential source (414) to the center of the coil. Momentum carries the electrons through the magnet and on into the core of the reactor. The electron energy is transferred to ions through the action of the potential well. The well has the feature that the magnitude of the ion's energy is approximately equal to the magnitude of the incoming electron's energy.
The voltage of the power supply is selected to give the ions the optimum energy for fusing. Different fuel choices require different voltages. FIG. 1B shows a graph of the fusion cross-section for four useful fuel choices. The curve labeled “DT” (102) shows the cross-section for fusing ions of deuterium (D) with ions of tritium (T). This reaction has the highest cross-section among all the possible light element combinations. This is the fuel choice of the ITER project.
The “DD” curve (104) shows the cross-section for fusing deuterium ions with deuterium ions. The “DD” fuel choice has a lower cross-section than “DT.” Because of the lower cross-section, a D+D fueled power-reactor will be bigger in size than a D+T reactor producing the same power level. However, size is not the only selling point of a reactor design. Drawbacks with tritium fuel are that tritium is radioactive and expensive. These drawbacks are not shared with deuterium. Deuterium is stable and plentiful compared to tritium. D+D fuel is called an “advanced fuel” in the prior art.
A major advantage of the subject invention over ITER is that, in some embodiments, the new design burns D+D fuel in a break-even reactor with a reactor size projected to be smaller than ITER. Avoiding the troublesome tritium as fuel is a great step forward from the prior art.
Returning attention to FIG. 1A, in the prior art the ion gun (460) is not shielded by the magnetic field. The ion gun attracts electrons and thus bleeds them from the confined plasma. To maintain the density and temperature of the plasma, lost electrons must be replaced by fresh electrons that draw energy from the high-voltage power supply. The input power required to replace the lost electrons reduces the power balance of the model reactor. Greater-than-unity power balance is needed for net-power operation. Power balance can always be increased by making the reactor larger. But then the resulting break-even Polywell reactor size would be even larger than ITER. Until solved by this invention, prior-art fueling solutions lead to unacceptably large reactor sizes.
Other features of the prior art, as indicated by FIG. 1A (205), (400), (405), (409), and (418), may prove useful in building and testing model reactors according to the invention. These features would function as described in 2010-Rogers, as incorporated herein.
It might be tempting to modify the 2010-Rogers design by moving the ion gun OUTWARD from where it is shown in FIG. 1A. If the ion gun were located behind the magnet, it would be better shielded by the magnetic field. The ions might then be shot inward along an axis of the cylindrical coil. To accomplish this, the velocity of the ions coming out of the ion gun would need to just match the height of the flank of the potential well at the position where they enter the core. The height of the flank of the potential dictates a magic velocity at which the ions can enter the well and be trapped. However, if the velocity is even a tiny amount higher than this magic velocity, the ions will fly across the well and escape the opposite side. The need for precise adjustment of the ion velocity results in an impractically small operating range for the reactor. The idea of moving the ion guns outside the magnets will not work due to this drawback.
The following “thought experiment” is proposed to illustrate the drawback: Suppose we wish to fill an extinct volcano with soccer balls. The volcano is like the potential well in an IEC reactor. The soccer balls are like fuel ions. The force of gravity is like the electrostatic force acting on the ions. We imagine the inside of the volcano as a perfectly smooth, frictionless bowl. The insides of the bowl rise to a circular rim all around. Outside the rim the flanks of the volcano fall away to level ground on all sides. The potential well is invisible in the IEC reactor; thus, we imagine the volcano to be invisible. Suppose it is shrouded in mist so that we cannot see it. We stand on level ground and kick the first ball toward the volcano. The ball rolls into the mist and then comes rolling back. Gradually, we kick the soccer ball harder and harder. Finally, we kick it hard enough that it rolls all the way up to the rim and falls into the volcano. But suppose we kicked it a little too hard. It rolls across the bowl, up the far wall, over the rim, and is lost. We adjust the strength of our kicks until some of the balls don't come back and don't exit the far side of the volcano. But even so, we still lose a lot of soccer balls. Minor variations in the strength of our kicks and in the height of the rim always cause most of the balls to be lost over the rim. Our efforts to trap all the soccer balls in the volcano are unsuccessful. And so is the problem of fueling Polywell with ion guns also intractable.
In addition to the problems described above, ion guns have another serious problem. They consume a lot of power to produce only a tiny amount of ion current. The typical ion gun, such as the commercial one shown in 2010-Rogers (FIG. 4G), produces a maximum current of around 0.1 microamperes of ions. The ion current needed to stabilize the plasma in small-scale Polywell is in the milliampere range. It would take thousands of ion guns operating in parallel to produce even 1 milliampere of ions. Needless to say, operating thousands of ion guns is not practical for a myriad of reasons.
The following conclusions summarize why existing ion sources are NOT suitable for fueling a Polywell type IEC reactor:
(1) The reactor can only operate in millisecond-pulse mode. If the pulse lasts longer than a millisecond, the high-voltage arcs and fries the magnets.
(2) Commercial ion sources are too big and too weak to be used inside the bore of the electromagnet. They cannot be shielded and they produce too little current.
(3) Injecting ions from external ion guns is impractical because the ions cannot efficiently cross the flanks of the potential well.
From the above analysis we see an apparatus for fueling an IEC reactor is needed. Without it fusion power cannot become a practical reality. The present patent application teaches how to build and use such an apparatus.